In the field of mining, large power operated machines carry a multiplicity of moving support blocks which carry ore or coal contacting bits usually referred to as pick bits. See, for example, U.S. Pat. No. 3,663,063; issued May 16, 1972 to Johanmeyer. Some of these bits are mounted with rectangular shanks and retained by various resilient clips. In many cases, however, these bits have a supporting shank which is circular in cross-section, the shank being supported in a block having a circular bore dimensioned such that the bit can rotate in its support. This rotation equalizes the wear around the bit and results in a longer life.
Circular bits of the type above described have, in some instances, been removably retained in the support socket by a split resilient retention ring which is lodged in an annular recess in the circular shank of the bit. The ring will compress circumferentially to allow it to pass into a support bore and has protuberances which expand into an annular recess in the wall of a bore which will provide axial engagement to retain the bit while permitting it to rotate in use. The U.S. Pat. No. 3,519,309, to Engel et al, issued July 7, 1970, illustrates a split ring resilient retainer of this type.
More recently a U.S. Pat. No. 4,201,421 to Den Besten et al, (May 6, 1980) has issued disclosing a combination retainer and wear sleeve which has an expanded dimension greater than the bore into which it is to be inserted and the bit shank has a shoulder to contact one end of the sleeve in a manner to retain the bit in the support bore due to the resilient frictional contact between the sleeve and the wall of the bore.
The present invention contemplates an improved split retention ring which can also serve as a wear sleeve. The retention ring is split at one end into a plurality of resilient projections separated by axial slots such that the resilient movement to enable the ring to move into a bore is in the projections and does not involve to any significant degree the basic circumferential resilience of the ring itself.
The construction of the resilient ring requires a stepped diameter construction in the bit shank such that a portion of the ring is supported on a larger diameter, and a smaller diameter portion directly adjacent the larger diameter is provided to receive the resilient projections when moved to an insertion position by the pressure of the wall of the bore. Upon reaching the operating position, the projections return to their normal circumferential position to have axial contact with an annular shoulder on the bit shank.
The improved design can utilize an almost continous collet enlargement to provide maximum wear area and thus is an improvement over the split rings which utilized localized protrusions which are easily damaged. A more rugged construction is thus possible while improved retention and bit rotation results.
The retention ring can also be applied to an extension of a drill steel to cooperate with a hollow drill bit such as used for drilling holes for roof support means in mining applications.
Other objects and features of the invention will be apparent in the following specification, including the claims in which the invention is described together with details to enable persons skilled in the art to practice the invention, all in connection with the best mode presently contemplated for the invention.